1. Field of the Invention
This invention relates to electrostatic chucks for retaining a semiconductor wafer in a semiconductor wafer processing system and, more specifically, to connectors for connecting power to an electrode embedded in a chuck.
2. Description of the Background Art
Numerous electrostatic chucks are known to the art for retaining a semiconductor wafer within a process chamber of a semiconductor wafer processing system. A semiconductor wafer processing system is disclosed in U.S. Pat. No. 4,842,683 entitled MAGNETIC FIELD-ENHANCED PLASMA ETCH REACTOR, David Cheng et al issued Jun. 27, 1989, and assigned to the same assignee as the present application, Applied Materials, Inc., of Santa Clara, Calif. This patent is incorporated herein by reference as if fully reproduced herein.
Specifically, the chuck 10 includes a chuck body 12 of ceramic material, such as for example aluminum nitride, and further includes an electrode 14 embedded in the chuck body 12, near the top portion thereof. The embedded electrode 14 may be, for example, a molybdenum mesh electrode. The electrode 14 is coupled to a power supply through an electrical coupler 16. The electrical coupler 16 includes a male connector member 18 and a female connector member 20, typically fabricated from molybdenum and beryllium copper, respectively. The chuck 10 is attached to a cooling plate 22 suitably mounted to the bottom of the chuck body 12 such as for example by a suitable adhesive or by suitable bolts not shown. The cooling plate 22 may be made, for example, of stainless steel or aluminum and is provided with a plurality of cooling channels 21 for carrying a liquid coolant for cooling the chuck 10. The male connector member 18 includes an upper solid cylindrical portion 24 extending through a bore 25 formed in the chuck body 12 and an integrally formed lower solid cylindrical portion 26 extending through a bore 27 formed in the cooling plate 22. Lower cylindrical portion 26 has a smaller diameter than the upper cylindrical portion 24. The female connector member 20 is provided with an inwardly extending upper cylindrical bore 28 forming a collet 29. The cylindrical bore 28 and collet 29 receive the lower cylindrical portion 26 of the male connector member 18 along path 37, thereby mechanically and electrically interconnecting the male and female connector members 18 and 20 together. The female connector member 20 is fixed within an insulator portion 11 of a pedestal base (not shown). The bottom of the female connector member 20 is connected to a source of RF biasing power 30 and a source of DC chucking voltage 32 by a connector 34 and a conductor 35.
Certain semiconductor wafer processes require that the chuck operate at a relatively elevated temperature, for example, from about 200xc2x0 C. to about 500xc2x0 C. Accordingly, the temperatures of the male and female connector members 18 are increased in the same temperature range with little reduction in temperature. Such components, especially the lower portion of the female connector member 20, which is coupled to the electrical connector 34 and conductor 35 for applying the RF and DC biasing voltage, must be able to withstand these operating temperatures. An undesirable outcome of operating a chamber at such elevated temperatures is an increase in the costs for manufacturing the connector and conductor, since they are generally not commercially available.
Accordingly, there is a need in the semiconductor wafer chuck art for a chuck that is operated at a relatively high temperature in the range noted above. Furthermore, there is a need for a connector for applying the DC chucking voltage and the RF biasing power to the chuck electrode, which includes thermal impedance that assists in reducing the heat transferred between the top portion of the connector and the bottom portion of the connector. Additionally, there is a need for a connector that will not be subjected to the detrimental effects of plasma that may form between the male and female portions of the connector or any other surface area, having a different voltage potential than the top portion of the connector.
An electrical coupler comprises an inner connector having upper and lower ends, the insulative outer connector element circumscribing the inner connector, and a thermally conductive flange disposed over the upper end of the inner connector and the outer connector for conducting heat from the electrical conductor.
In another aspect, a support assembly for supporting a semiconductor wafer comprises a chuck body having at least one electrode embedded therein, and a cooling plate positioned beneath the chuck body. An electrical coupler is positioned within the cooling plate and has a thermally conductive flange circumscribing the electrical coupler and disposed upon a surface of the cooling plate.